I have set up my WDMB (white led edition) as a domain member.
I created a new shared folder.
I wan't to restrict access to this folder so that only users of a certain group can access it.

In the network storage manager, in advanced mode, I went to the users > folder share permissions pannel.
I removed "public access" and added my group (say, MYDOMAIN\mygroup) with "full access" privileges.
This works until I shutdown and restart the WDMB. After restarting, I am prompted for a password when trying to access the share.
If I go back to the users > folder share permissions pannel and do anything in here (add a user with only read access for instance) and submit the changes, then I can access the share without being prompted for the password.
I can then go back and set the right permissions and everything works as expected.